Orthogonal Frequency Division Multiple Access technology (OFDMA) is widely used in new generation of wireless network, for example, Long Term Evolution (LTE) project of the 3rd Generation Partnership Project (3GPP) and Worldwide Inter-operability for Microwave Access (WiMAX) system. In a multiple-cell network, although OFDMA provides frequency diversity and sub-channel power control, interference among edge channels of cells still exists. Frequency reuse is an important method for increasing system capacity, promoting energy efficiency and reducing interference.
At present, a classic frequency reuse factor has several specific options, such as 1, 3, 4, or 7, etc. Frequency reuse factor of 1 represents that neighbor cells use same frequency resource; however, the co-channel interference is serious at edge of cells. Frequency reuse factor of 3 represents that three neighbor cells use different frequency resource; in this case, co-channel interference does not exist among the three cells, but frequency efficiency will be dropped to one-third. Because the requirement in new generation of mobile communication system is high, designing a reasonable method for frequency reuse is necessary. Partial Frequency Reuse (PFR) and Soft Frequency Reuse (SFR) are two new methods for frequency reuse. For PFR, a cell is divided into two parts. In scenario of three sections, the frequency reuse factor of cell central users is 1, while the frequency reuse factor of cell edge users is higher. This solution can highly improve cell edge performance; however, the average throughput of the cells decreases seriously since the reuse factor of the edge users is 3. For the SFR, each cell can use all subcarriers and determine the extent of using a frequency by setting a transmission power threshold; the frequency reuse factor of the system can realize smooth transition. Because the reuse factor of the SFR solution is 1, the average throughput of its cells is better than that of the cells of PFR. However, the performance of SFR will be decreased rapidly with the increase of loading of the system.
The methods as mentioned above are dedicated to guaranteeing higher system spectrum efficiency and relatively low interference among cells as well. Generally, an enhanced frequency reuse solution is, on the basis of classic frequency reuse, improving a certain performance of system, such as average spectrum efficiency of cells, etc., to some extent. For problem of balancing system spectrum efficiency and interference among cells, more effective frequency policies are required in the new generation of wireless cellular network.